Calculate common rafter length based on roof pitch and run.
Roof Dimensions
Cut Specifications
Cutting Rafters?
Enter the run and pitch to find the exact length needed.
About this calculator
Overview
This calculator determines the length of a common rafter, which spans from the ridge board to the wall plate. It accounts for the ridge board thickness and overhang to give you the precise cutting length.
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Pro Tips
Always measure the run horizontally from the outside of the wall plate to under the ridge.
Remember to deduct half the thickness of the ridge board from the total run.
Buy lumber longer than the calculated length to account for the angle cuts and overhang.
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Fun Facts
"Roof pitch is typically expressed as ratio x/12, meaning 'x' inches of rise for every 12 inches of run."
"The 'Birdsmouth' cut is the notch where the rafter sits on the wall plate."
"Standard lumber comes in 2-foot increments (8', 10', 12', etc.)."
